Tapahtumanlähteisiin

Tapahtumanlähteisiin, often translated as "event sourcing," is an architectural pattern where all changes to application state are stored as a sequence of immutable events. Instead of storing the current state of data directly, the system logs every event that has occurred. To reconstruct the current state, one simply replays all the events in chronological order. This approach offers several advantages, including a complete audit log of all data modifications, enabling point-in-time reconstruction of the application's state.

The core principle of event sourcing is immutability. Once an event is recorded, it cannot be altered or deleted. New events are always appended to the event log. This makes it easier to understand how the application's state evolved over time. It also simplifies debugging, as developers can examine the sequence of events leading up to a particular state. Furthermore, event sourcing can facilitate complex queries and analytics, as the historical data is readily available.

Implementing event sourcing typically involves an event store, which is a database optimized for storing and retrieving sequences of events. The application's domain logic then processes commands, which trigger events. These events are persisted in the event store, and then consumers can subscribe to these events to update their own read models or trigger other side effects. This pattern is particularly well-suited for systems that require high traceability, auditing capabilities, or complex state transitions.